1. Field of the Invention
The invention relates to an air filtering apparatus, for providing filtered air to an enclosed space, including a filter mounting device for sealing the filter within the air filtering apparatus.
2. Description of the Prior Art
In enclosed spaces, or rooms, which contain delicate and sensitive computers and other control instrumentation, it is desirable to provide a clean, pressurized environment for such rooms. Examples of such enclosed spaces, or rooms, are computerized control rooms located in petrochemical refineries, chemical plants, pulp and paper mills, or other areas where corrosion and dust particles pose a hazard to computers or other delicate instrumentation. The clean, pressurized environment may be provided by air filtering apparatus which takes fresh, outdoor air, along with return room air, and passes it through an apparatus which includes a plurality of various types of filters which are designed to filter out undesired chemicals and/or particulate materials, whereby filtered and/or pressurized air may be provided to the enclosed space or room. These prior art air filtering apparatus may include different types of filters, such as: chemical filters, having an impregnated activated alumina media; high efficiency particulate arrestance ("HEPA") filters; and conventional non-woven cotton fabric type filters. With presently designed air filtering apparatus, a problem exists with respect to sealing the various types of filters within the air filtering apparatus, and in particular sealing chemical and HEPA filters within the air filtering apparatus. It is desired that all the air to be filtered passes through the various filters, and is not permitted to pass through the air filtering apparatus without passing through such filters. In the case of chemical and HEPA filters, such filters are disposed in metallic housings, or enclosures, and are adapted to be placed within the filtering apparatus and sealed with respect thereto, so that all the air which passes through the air filtering apparatus, passes through each of the various filters. After these filters are placed within the air filtering apparatus, they must be disposed in a sealing relationship within the air filtering apparatus.
Various methods have been proposed to mount such filters within the air filtering apparatus, and to sealingly dispose such filters within the air filtering apparatus. One of the most common methods is the use of strips of felt or nylon pile gasketing in the portion of the air filtering apparatus which receives the replaceable filters. In this regard, conventional filters must be routinely inspected and/or cleaned on a scheduled basis, as well as must eventually be replaced with a new filter. Conventional air filtering apparatus may have "filter tracks" into which the filters are slid into place into the air filtering apparatus. The felt or nylon pile gasketing is secured in the filter tracks to fill the voids between the filter and the filter tracks. These materials typically do not completely fill the gap between the surface of the filter tracks and the filter, particularly at the corners of the filters. The use of such gasketing material in the filter tracks may be particularly ineffective when it is desired to provide substantial filtering of the air being provided to a room containing computers, or other sensitive instrumentation. For example, the efficiency of some HEPA filters is rated at 99.97% efficiency when arresting, or filtering out, particles as small as 0.3 microns (0.000017 inch) in diameter, and some chemical filters are rated so as to provide the reduction of some contaminants to levels as low as 5 parts per billion. Accordingly, when it is desired to provide such substantial filtering, the desired objective is not achieved if air which is intended to be filtered by passing through such filters, instead can bypass the filter by leaking through the seals disposed at the corners of the filters and the filter tracks. Another disadvantage with the use of strips of gasketing material, against which the filter slides as it is being inserted into the air filtering apparatus, is that these sealing strips may wear rapidly with repeated use, as when the filters are cleaned and inspected, which thus further reduces the integrity of the air filtering apparatus.
Another method to provide sealing between the filter and the air filtering apparatus has been the use of foam gasketing material disposed between a filter and a frame in which the filter is disposed. The filter is clamped against the gasketing material by the use of a plurality of thumb screws or bolts, which are tightened to compress the filter against the foam gasket material, in a manner similar to that which is used to seal an oil pan of an automobile to the engine of the automobile. The use of a plurality of thumb screws or bolts can provide a sufficient seal between the filter and the air filtering apparatus, provided maintenance personnel servicing the filters exercise sufficient care to evenly tighten the bolts and/or thumb screws, so that equal pressure is exerted on the filter frame about its periphery, in a manner similar to that used when securing an oil pan to the engine of a motor vehicle. The problem with the use of a plurality of thumb screws and/or bolts is that typically the bolts and/or thumb screws are not evenly tightened and the resulting seal may not be effective in insuring that unfiltered air does not ultimately pass through the ineffective seal and through the air filtering apparatus, without having been filtered. If the bolts of an oil pan are not evenly tightened to apply an equal amount of pressure about the periphery of the oil pan, the fact that the seal is not properly made becomes readily apparent, in that oil will begin to leak. The fact that a proper seal has not been effected within an air filtering apparatus, between the filter and the air filtering apparatus, may not be so readily apparent, particularly when the intent is to filter out particles as small as 0.3 microns in diameter. Additionally, the procedure of tightening the plurality of thumb screws and/or bolts is very time consuming, since a great number of bolts and/or thumb screws are often required. The procedure of tightening the bolts and/or thumb screws is also made more difficult when a chemical filter is being installed and/or serviced or inspected, in that many chemical filters can weigh several hundred pounds.
Accordingly, prior to the development of the present invention, there has been no air filtering apparatus, or filter mounting device for use in an air filtering apparatus which: efficiently and easily provides an effective seal between a filter and its mating surface within an air filtering apparatus; does not slide a filter against a strip of gasketing material, which can cause undesired wear upon the strip of gasketing material; and provides an indication if a proper seal for the filter has not been made. Therefore, the art has sought an air filtering apparatus and a filter mounting device which: efficiently and easily provides an effective seal between a filter and its mating surface within an air filtering apparatus; does not require the filter to slide against, and potentially wear out, a strip of gasketing material; and provides an indication to maintenance personnel that the desired seal has not been effected.